Hepatocyte growth factor (HGF) was first discovered as a protein which promoted the growth of rat hepatocytes in primary culture and was later cloned. HGF was also found to be a multifunctional factor that promotes proliferation, motility and morphogenesis in epithelial cells, and has since been found to have effects on stromal cells and multipotent cells from a number of other tissues, including cartilage. While HGF has been shown to have beneficial effects in several studies, the usefulness of HGF has been limited by several factors. First, the half-life of HGF in the body is extremely short, estimated at around five minutes. This precludes the effectiveness of a simple injection of the compound, or passive adsorption onto a dense surface for most purposes. (Hossain, M., et. al., Hepatocyte Growth Factor (HGF) Adsorption Kinetics and Enhancement of Osteoblast Differentiation on Hydroxyapatite Surfaces. Biomaterials (2005) 26:2595-2602). Second, the primary receptor of HGF, c-MET, is believed to be implicated in the invasiveness of some types of tumors, raising concerns about the safety of HGF in large doses. Some studies have suggested that HGF may discourage desirable cell differentiation, such as osteogenesis. This is believed to be a function of concentration. (Wen, Qian, Change in Hepatocyte Growth Factor Concentration Promote Mesenchymal Stem Cell-mediated Osteogenic Regeneration. J. Cell. Mol. Med. (2012) 16(2):1260-1273). Accordingly, it is desirable to provide a method for delivering HGF in low but effective doses specifically to the desired therapeutic site. Additionally, it may be desirable that the concentration of HGF diminish relatively rapidly over time. (Kawasaki, Tishiki, et. al., The Effect of Timing in the Administration of Hepatocyte Growth Factor to Modulate BMP-2-induced Osteoblast Differentiation. Biomaterials (2010) 31:1191-1198).
Hyaluronic acid (HA), or hyaluronan, is a linear polysaccharide that consists of alternating units of a repeating disaccharide, β-1,4-D-glucuronic acid-β-1,3-N-acetyl-D-glucosamine. HA is found throughout the body, from the vitreous of the eye to the extracellular matrix (ECM) of various tissues. HA is an essential component of the ECM, believed to be involved in cellular signaling, wound repair, morphogenesis, and matrix organization. Additionally, HA is rapidly turned over in the body by hyaluronidase, with half-lives ranging from hours to days. HA and its derivatives have been used clinically in a variety of applications. For example, HA in an injectable form is used routinely in ocular surgery, as a dermal filler, and in the treatment of arthritis of the synovial joints.
It has been shown that the addition of HGF to a semi-synthetic hydrogel containing HA chemically cross-linked with a number of other components allowed the continued delivery of HGF over several days. (Zhao, Jing, et al., Recruitment of Endogenous Stem Cells for Tissue Repair. Macromol. Biosci. (2008) 8:836-842). However, such hydrogels are chemically complex, contain synthetic materials, may be difficult for cells to remodel due to the extensive cross-linking with synthetic materials, and may retain HGF for too long a time. They may also be mechanically inappropriate for certain applications. For example, such hydrogels alone may be mechanically too weak for tissue repair applications. (Burdick, Jason A., et. al., Hyaluronic Acid Hydrogels for Biomedical Applications. Adv. Mater. (2011) 23:H41-H56). On the other hand, such gels may be too viscous and resistant to dispersion for use in an injectable therapy, such as in the synovial joints.
Therefore a need remains for preparations which will allow the beneficial delivery of HGF across a variety of surgical applications.